EAST MILLINOCKET, Maine — What was likely an outbreak of norovirus left Schenck High and Opal Myrick Elementary schools with 28 percent of students missing classes on Tuesday, one of the higher single-day school absentee rates recorded in Maine this year, officials said Friday.

Two teachers and an estimated 78 students called in sick on Tuesday at the Schenck building, which houses about 280 students, including about 140 from the K-4 school located in one of its wings. School officials believe norovirus was the likely cause, Schenck Principal John Farrington said.

Dr. Stephen Sears, state epidemiologist with the Maine Center for Disease Control and Prevention, called the 28 percent one of the higher single-day absentee rates he has heard of.

“That is definitely higher than what we normally see,” Sears said Friday.

Under state law, school nurses must report to Maine CDC absentee rates higher than 15 percent, he said. Sears speculated that the mixing of young and teen students at Schenck, which has occurred there since September 2011, contributed to the high rate.

“A lot of times there are multiple causes for that, all of the different diseases that can happen,” Sears said. “If this is norovirus, which is likely — we haven’t tested for it in this case — then the biggest problem with it is that it is highly contagious.”

A nasty stomach bug, norovirus is also known as “winter vomiting disease.” Its primary symptoms: intense bouts of nausea, vomiting, diarrhea and stomach cramping that typically last 24 to 48 hours. It was identified as the culprit in half of 16 outbreaks reported in a Maine CDC advisory in January.

A group of related viruses, noroviruses are found in the vomit and stool of infected people. The viruses are highly contagious and spread easily in tight quarters such as hotels, schools, long-term care facilities, airplanes and cruise ships.

Exposure can result through direct contact with someone who is ill, by consuming food or drinks handled by an infected person, and by touching contaminated objects or surfaces, where the viruses can linger for prolonged periods.

School custodians have been cleaning water fountain buttons, door knobs, desks and all other common areas several times daily to prevent infections, Farrington said. Extra attention is paid to the desks of ailing children and school staff and students are encouraged to avoid personal contact and use hand-sanitizing stations frequently.

“That is something they encourage them to do all the time, anyway,” Farrington said.

School officials notified parents to keep ill children home until they had been free of symptoms for 24 hours, as norovirus can recur after appearing to lapse, Farrington said.

As of Friday, the absentee rate at Schenck and Myrick had fallen to 15 percent. The rate appears likely to drop further on Monday, Sears said.

Norovirus and influenza most commonly hit during winter. From late November to Feb. 5, during the most recent of what is typically an annual outbreak, 32 Maine schools reported absentee rates of 15 percent or greater, Sears said.

Tuesday’s absentee rate at Schenck and Myrick “was as high as I have ever seen in 10 years as an administrator,” Farrington said.

Absentee rates, Sears said, are a difficult measure to judge schools by, given the wild fluctuation of school populations that have occurred with the general depopulation of northern Maine over the last several years.

The most devastated single classroom at Schenck and Myrick was that of first-grade teacher Angela Pelkey. She had five students instead of her usual 11, Farrington said.

“I hope this is over with,” he added.